1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Description of the Related Art
Silicon carbide (SiC) has a band gap that is about three times as large as that of Si, and a breakdown field strength that is about ten times as high as that of Si. The silicon carbide thus enables a sharp reduction in on resistance.
However, if a gate oxide film in a MOS transistor made of SiC is formed by a normal thermal oxidation method, the transistor disadvantageously offers a high interface state density. Thus, the channel mobility of the MOS transistor exhibits a very small value of several cm2/Vs.
To solve this problem, a method has been proposed which forms a gate oxide film by wet oxidation and then reduces temperature with a wet oxidation atmosphere maintained intact (see JP-A 2007-96263 (KOKAI)). This method enables formation of a MOS transistor exhibiting a channel mobility of about 50 cm2/Vs and a flat band shift of about 5 V.
However, even the MOS transistor formed by the above-described method fails to offer sufficient characteristics including a high channel mobility and a low flat band shift. Thus, the conventional art has difficulty providing an SiC-MOS transistor with excellent characteristics.